CN104246255B

CN104246255B - Rolling bearing component

Info

Publication number: CN104246255B
Application number: CN201380016441.4A
Authority: CN
Inventors: 埃德加·施特赖特; 奥斯卡·贝尔
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2012-03-30
Filing date: 2013-03-07
Publication date: 2017-05-10
Anticipated expiration: 2033-03-07
Also published as: JP2015511692A; JP6211051B2; EP2831436B1; RU2629517C2; US9416822B2; EP2831436A1; RU2014143849A; DE102012205242A1; WO2013143817A1; CN104246255A; US20150049973A1

Abstract

The rolling bearing component (2, 3, 4) has the following characteristics: -a nitrided edge region (5) with a nitrogen content decreasing from the outside inwards, -a core region (6), -a residual compressive stress decreasing from the outside inwards in the edge region (5), -an edge hardness of 870HV 0.3 to 1000HV 0.3 in a depth of 0.04mm, wherein-the hardness in a depth of 0.3mm is at most 250HV 0.3 less than the edge hardness.

Description

Rolling bearing component

Technical Field

The invention relates to a rolling bearing component, in particular to a bearing ring of a rolling bearing.

Background

Machine elements for rolling loads are known, for example, from EP 1774187B 1 and from EP 1774188B 1. The invention relates to a rolling bearing element, in particular a bearing ring, made of steel having a martensitic structure, having a thermochemically produced, nitrogen-rich boundary layer.

Disclosure of Invention

The object of the present invention is to further improve the rolling bearing component with respect to the mentioned prior art.

According to the invention, this object is achieved by a rolling bearing component having the features of claim 1. The rolling bearing component is preferably designed as a bearing ring and has the following features:

-a nitrided (auxgestint), edge region with decreasing nitrogen content from the outside inwards,

a core region having an at least approximately constant stiffness,

a residual compressive stress (Druckeigenspannung) which decreases from the outside to the inside in the edge region,

a hardness of 870HV 0.3 to 1000HV0.3 in a depth of 0.04mm (in the following also referred to as edge hardness),

wherein,

hardness in depth of 0.3mm is at most 250HV 0.3 less than edge hardness.

The invention proceeds from the idea that in applications where safety is important, for example in machine elements in air transport, a high degree of damage tolerance is required in addition to the service life which is as high as possible. If, in individual cases, small damage occurs, in particular locally, the functional action of the machine element must be maintained at least until the corresponding device can be stopped without danger (for example, in the case of an aircraft, the target airport is reached). For this reason, a high damage tolerance of all components is required in addition to the early identification of the incipient damage as possible.

In the case of rolling bearing components having a carburized edge region, the residual stress distribution is also defined by a hardness of at least 870HV 0.3 and at most 1000HV0.3, defined according to the invention, with respect to a depth of 40 μm, to such an extent that the shear stress occurring in the event of a failure of the nitrided zone caused by damage is defined such that the shear stress occurring in the event of a failure of the nitrided zone is defined such that the roll-over stressThe damage propagation in the lower zone is not significantly faster than in the case of the non-nitrided edge zone. Furthermore, nitrided materials with increased hardness also lose ductility; reduced ductility also means less resistance to damage propagation.

By the illustrated boundaries of the edge hardness and by defining the maximum difference between the minimum hardness in the core region and the edge hardness as 250HV 0.3, a component is provided which in an optimal manner complies with the requirements for high resistance against the development of damage (i.e. sufficient hardness and residual compressive stress) and at the same time the requirements for resistance to the propagation of damage (i.e. high ductility and not too high residual stress). In the depth of 0.3mm, the hardness in HV0.3 is greater than preferably 75%, in particular 80%, of the hardness in the depth of 0.04 mm. In an advantageous embodiment, the absolute value of the residual compressive stress on the surface of the rolling bearing component is at least 500MPa and at most 1000 MPa. The value of the residual compressive stress in a depth of 0.05mm is less than preferably 60%, in particular 50%, of the value of the residual compressive stress at the surface.

The residual compressive stresses in the edge regions of the rolling bearing component are present at least in the mechanically unloaded state of the rolling bearing component, wherein all statements relating thereto in the dependent claims also relate to the mechanically unloaded state of the rolling bearing component.

In a preferred embodiment, a depth below 80% of the maximum value of the nitrogen content in the edge region corresponds to a residual compressive stress of at least 1.75 times, in particular at least 2 times, for example 3 times, the depth of 80% of the maximum residual compressive stress.

The depth below 80% of the maximum value of the nitrogen content in the edge region, i.e. the so-called 80% nitrogen boundary, corresponds to a depth of the residual compressive stress below 80% of the value of the maximum residual compressive stress in the edge region (80% residual compressive stress boundary), preferably up to 8 times, in particular up to 4 times. Thus, according to different possible embodiments, the 80% nitrogen boundary is located in the range between 1.75 and 4 times or in the range between 2 and 4 times or in the range between 3 and 4 times or in the range between 1.75 and 8 times or in the range between 2 and 8 times or in the range between 3 and 8 times of the 80% residual compressive stress boundary.

By the mentioned definition of the hardness and the hardness difference while the distribution of the residual compressive stress and the nitrogen content is bounded in the described manner, a rolling bearing component is provided which likewise complies with the competing requirements for ductility and hardness. In particular, a high tolerance against the development of local interruptions ("damage") of the nitrided zone under overturning stresses and a long service life under difficult conditions, such as the presence of contamination in the oil flow, are given.

The metallic material of which the rolling bearing component is made is, for example, steel with the designation M50(AMS 6490/6491, 80MoCrV 42-16) or M50NIL (AMS 6278, 13MoCrNiV 42-16-14). Other materials that can be used are described in the prior art cited at the outset.

Drawings

Embodiments of the invention are explained in detail below with the aid of the figures. Wherein:

fig. 1 shows a first rolling bearing in a schematic sectional view;

fig. 2 shows a bearing ring of a second rolling bearing in a cross-sectional view;

fig. 3 shows a schematic representation of the formation of shear stress in the case of interrupted layers with residual stress;

fig. 4 shows the hardness distribution of the rolling bearing member;

fig. 5 shows the residual stress distribution of the rolling bearing component according to fig. 4;

fig. 6 shows the nitrogen distribution of the rolling bearing component according to fig. 4.

Detailed Description

Fig. 1 shows, in section, a rolling bearing, generally designated by reference numeral 1, namely a ball bearing, which has bearing rings 2, 3 (i.e. an inner ring 2 and an outer ring 3, which are generally referred to as rolling bearing components 2, 3) and rolling bodies 4, which are also assigned to the concept of rolling bearing components. In this case, all the rolling bearing members are made of a metallic material.

Each rolling element 4 is formed from steel having a martensitic structure and has a thermochemically produced, nitrided edge region 5 and a core region 6 differing from the edge region with regard to a plurality of parameters, in particular the chemical composition. The transition between the edge region 5 and the core region 6 is marked in fig. 1 by a dashed line, the position of which, as is shown in the overall illustration, is not to scale.

In the edge region 5, there is a compressive residual stress which decreases from the outside to the inside, wherein the boundary (at which 80% of the maximum compressive residual stress is lower) is referred to as the 80% compressive residual stress boundary and is designated 80 in the figure_σAnd (4) showing.

The nitrogen present in the edge regions 5 likewise decreases from the surface of the rolling elements 4 inwards. The boundary (at which 80% of the maximum nitrogen concentration is below) is referred to as the 80% nitrogen boundary, and is shown as 80% in the figure_NAnd (4) showing. 80% Nitrogen boundary 80, measured from the surface of the Rolling elements 4_NAt 80% residual compressive stress boundary 80_σAt least 1.75 times the depth, for example 2 times the depth, in particular 3 times the depth. In the edge region 5, the hardness of the rolling elements 4 is 870HV 0.3 at a minimum and 1000HV0.3 at a maximum with respect to a depth of 40 μm. The mentioned depth of 40 μm is preferably located at the 80% residual compressive stress boundary 80_σAnd 80% nitrogen boundary 80_NIn the meantime. The hardness in the core region 6 is at most 250HV 0.3 less than the hardness in the edge region 5.

The rolling bearing 1 according to fig. 2 can be used, for example, as a bearing in a gas turbine. The properties of the bearing rings 2, 3 of the rolling bearing 1 according to fig. 2 (which relate to the material parameters described above) correspond to the properties of the rolling elements 4 of the exemplary embodiment according to fig. 1. In this case, the hardness of the rolling bearing component 2, 3 in a depth of 40 μm is also in particular a minimum of 870HV 0.3 and a maximum of 1000HV 0.3. Likewise, the hardness of the rolling bearing components 2, 3 in the core region 6 in a depth of 0.3mm is likewise at most 250HV 0.3 less than in the edge region 5.

Fig. 3 shows the derivation of the shear stress in the case of interrupted layers with residual stress. The rolling bearing component 4 visible in fig. 3 is a rolling element 4 according to the exemplary embodiment of fig. 1, wherein fig. 3 shows a schematic representation of the damage of the nitrided edge region 5. As shown in fig. 2, the rolling bearing component 4 according to fig. 3 can likewise also be a bearing ring 2, 3. As can be seen in fig. 3, if the nitrogen-rich layer, i.e. the edge region 5, is locally interrupted, no stress acts on the interrupted region (free surface). In this case, residual stress is otherwise understood as an average value for the layer thickness.

Within a certain angular range Φ, the residual stress (normal stress) increases continuously up to the residual stress in the undisturbed zone. For balancing reasons, the increased residual stress in this region must lead to an additional shear stress τ. This additional shear stress τ contributes to a further improvement of the damage. The higher the residual compressive stress in the edge region 5, the higher the shear stress which occurs in the event of failure. The residual compressive stress in the nitrided edge layer 5 of the rolling bearing component 4 is in turn related to the structural hardness.

Fig. 4 shows the hardness distribution of the rolling bearing component 4 according to fig. 3 with the edge hardness according to the invention. As can be seen from fig. 4, the edge hardness is 950HV 0.3. The hardness value reduced by 250HV 0.3, i.e. 700HV, is clearly exceeded in all regions of the rolling bearing component 4 (see detail a in fig. 3). It is also known from fig. 4 that the hardness in HV0.3 is greater than 75% of the hardness in depth of 0.04mm (i.e. the edge hardness) in a depth of 0.3mm (see detail b).

Fig. 5 shows the residual stress distribution in the rolling bearing component 4 according to fig. 3. On the surface of the rolling bearing member 4, the residual compressive stress has an absolute value of 800MPa (see c for details). 80% residual compressive stress boundary 80_σIn a depth of between 0.005mm and 0.02 mm. In the depth of 0.05mm, the value of the residual compressive stress has dropped to less than half the absolute value of the residual compressive stress on the surface of the workpiece (see d for details). In the case of a depth of the rolling bearing component 4 of more than 0.3mm, there is a residual tensile stress (zugeigen span) which is very small in absolute value compared to the residual compressive stress in the edge region 5.

Fig. 6 shows the nitrogen content distribution in the rolling bearing component 4 according to fig. 3. The nitrogen content is between 1.5% and 2.0% on the surface of the workpiece (see e in detail; in wt%). The nitrogen content decreases continuously from the surface of the workpiece. 80% Nitrogen boundary 80_NIn a depth of between 0.02mm and 0.04 mm.

The nitrided edge region 5 with the described properties provides a very favorable configuration of hardness and residual compressive stress for the overturning stress, not only in operation under difficult conditions but also in the event of local damage to the layer.

List of reference numerals

1 rolling bearing

2 bearing ring, rolling bearing component

3 bearing ring, rolling bearing component

4 rolling element and rolling bearing member

5 edge zone

6 core region

σ_eig(general) residual stress

σ_eig,maxResidual stress in unaffected nitrided layers

Phi angular range within which residual stresses build up

d phi angular range variation

Radius of R nitrided layer

thickness of t-nitrided layer

Tau shear stress

80_N80% nitrogen boundary

80_σ80% residual compressive stress boundary

Claims

1. A rolling bearing component (2, 3, 4) having the following features:

a nitrided edge region (5) with a nitrogen content decreasing from the outside inwards,

-a core region (6),

-a residual compressive stress decreasing from the outside inwards in the edge region (5),

-a hardness in the depth of 0.04mm of 870HV 0.3 to 1000HV0.3,

wherein,

-hardness in depth of 0.3mm is at most 250HV 0.3 less than hardness in depth of 0.04 mm.

2. Rolling bearing component (2, 3, 4) according to claim 1, characterized in that in a depth of 0.3mm the hardness in HV0.3 is greater than 75% of the hardness in a depth of 0.04 mm.

3. Rolling bearing component (2, 3, 4) according to claim 1, characterized in that the absolute value of the residual compressive stress on the surface is at least 500MPa and at most 1000 MPa.

4. Rolling bearing component (2, 3, 4) according to claim 3, characterized in that the value of the residual compressive stress in a depth of 0.05mm is less than 60% of the value of the residual compressive stress at the surface.

5. Rolling bearing component (2, 3, 4) according to any of claims 1 to 4, characterized in that the depth (80) is below 80% of the maximum value of the nitrogen content in the edge region (5)_N) Corresponding to a depth (80) at which the compressive residual stress is 80% of the maximum compressive residual stress_σ) At least 1.75 times.

6. Rolling bearing component (2, 3, 4) according to claim 5, characterized in that the depth (80) is below 80% of the maximum value of the nitrogen content in the edge region (5)_N) Corresponding to a depth (80) at which the compressive residual stress is 80% of the maximum compressive residual stress_σ) Up to 8 times.

7. Rolling bearing component (2, 3) according to claim 5, characterized in that it is configured as a bearing ring (2, 3).

8. Rolling bearing component (4) according to claim 5, characterized in that it is configured as a rolling body (4).

9. Rolling bearing having a rolling bearing component (2, 3, 4) according to claim 7 or 8.